Soak tamarind in some warm water for 20 minutes. Mash & drain the water in a separate bowl by removing the pulp. 

Pressure cook toor dal with 1 cup of water with enough water and turmeric powder till its soft and cooked properly. Mash the lentil and keep it aside. 

Slice the bitter gourd and remove the seeds.

Add 1 tsp of oil in a frying pan and roast the channa dal, coriander seeds, red chillies, pepper corn. Add freshly grated coconut and roast till light brown. Allow this mix to cool down and then add it to your grinder and blitz it to make a smooth paste by adding little water to it. 

Add chopped bitter gourd in a wok with 1 tsp oil and saute in a low flame for 2 minutes.

Add tamarind water, turmeric powder, jaggery and let it cook on low flame for few minutes.

Now add grounded paste with cooked lentil. Mix well. Add water to adjust consistency.

Add salt to taste and mix it well.

Add oil in a small frying pan and when its warm add mustard seeds. When mustard seeds splutter, add a pinch of asafoetida, curry leaves and saute. Add this tempering in the Pitlai and serve it hot with some rice.